1. Field of the Invention
The present invention relates to a clamping nut located in a rotatable manner on the outer surface of a clamp object member, for clamping or releasing the clamp object member. This invention also relates to a tool holder with this clamping nut and a spanner for causing the clamping nut to rotate and clamp the clamp object member.
2. Description of the Related Art
various kinds of conventional clamping nuts are known for clamping a clamp object member by mounting any of the clamping nuts on the outer surface of the clamp object member and causing the clamping nut to rotate. On the inner surface of this clamping nut, a converting part (such as a screw) is formed for the conversion of the rotary motion of the clamping nut into that of rectilinear motion. This rectilinear motion causes the clamping nut to move back and forth in the axial direction of the clamp object member, thereby clamping or releasing the clamp object member.
One example of utilization of this clamping mechanism is as a tool holder which includes: a tool holder body for holding a tool through the medium of a collet; and a clamping nut mounted in a rotatable manner on the tool holder body, for clamping both the tool holder body and the collet by means of rotary motion.
The tool holder of this structure typically has a screw, and a needle roller part or the like that is formed on the inner surface of the clamping nut, for the purpose of converting the rotary motion into rectilinear motion. Moreover, on the outer surface of the clamping nut, knurling is applied and a concave part or an engagement groove is formed for the purpose of engagement with the spanner for rotation of the clamping nut. The spanner is made to engage with the concave part or the engagement groove of the clamping nut and causes the clamping nut to rotate. Accordingly, the clamping nut is used to clamp the tool holder body, thereby causing the tool holder body to securely hold the tool.
An example of such tool holders includes one described in Japanese Utility Model Laid-Open (Kokai) Publication No. HEI 5-26208 A tool holder (or chuck) described in this publication is constructed in a manner such that the outer surface of a clamping nut (or outer sleeve) mounted on a tool holder body (or chuck body) is formed as a complete cylindrical surface without any groove or knurl for engagement with a spanner, and this complete cylindrical surface is the section where the belt of a belt spanner is to be wound. Since the structure of this tool holder has no such groove for the purpose of engagement with the spanner, because a groove may cause the tool holder to be thrown off the dynamic balance at the time of high-speed rotations, it has the advantageous effect of enhancing the dynamic balance, eliminating any wind noise that is unavoidable at the time of high-speed rotations, and drastically reducing chattering vibrations.
However, concerning the above-described conventional tool holder, as the spanner is used to rotate (or fasten) the clamping nut, the fastening force is imparted together with the rotational force and operates in the radial direction of the clamping nut towards the inside of the clamping nut, thereby pressing, from the outer surface of the clamping nut, the screw or the needle roller part formed on the inner surface of the clamping nut. Accordingly, the frictional force that exists at this part increases, and it becomes difficult to rotate the clamping nuts thereby lowering work efficiency. There is also the possibility that the clamping force of the clamping nut will weaken and it becomes difficult to cause the tool holder to firmly hold the tool.